Synthesis of esters of thioldimethylvaleric acid



at higher temperatures under increased pressure. The hydrolytic agent employed may be any of the various alkaline agents, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, bariumhydroxide, sodium carbonate, potassium carbonate, etc. ForV reasons of economy the alkali metal hydroxidea e. g., sodium hydroxide, are Vusually preferred. The aqueous alkaline agent may be of any concentration ranging from as low as about 0.5. per cent by weight to about 50 per cent by weight or even higher. We have found, however, that more con-` centrated solutions are preferred in that they favor rapid hydrolysis of the CaHizvSs compound. The alkaline agent is usually employed in an amount representing between about 4 and about 8 moles of the alkali per mole of the sulfurized diisobutylene. More than 8 moles may be used but is not necessary insofar as completeness of the reaction is concerned. The time required for completionof vthe reactiony depends upon the particularaqueousalkaline agent employed and its concentration and upon thetemperature employed. Ordinarily, however, the reaction is completed in'from about 0.5 to 25 hours.

Upon completion of the alkaline hydrolysis the reaction mixture is cooled to a temperature of about 20 to 30 C. When a dialkyl sulfate is employed, temperatures of the order of 20 to 30 C. favor the utilization of only one alkyl group in the formationof the alkyl ester. The other alkyl group is boundup as the alkyl alkali metal sulfate. While temperatures greater than 30 C. ordinarily favor. utilization of the second alkyl group as an alkylating agent, higher temperatures have a disadvantagein that the yield of the alkyl thiolesterrmay not be as high as that obtained at temperatures Vbelow 30 C. The alkyl sulfate in an amount equimolar to the amount of alkaline agent employed,A that is, one mole of dialkyl sulfate for each mole of alkali used and a neutral solvent are then added to the cooled hydrolysis reaction mixture. While the presence of a neutral solvent is not necessary to obtain reaction between the .alkali salt of thioldimethylvalerio acid of the reaction mixture and the alkyl sulfate, we have'lfou'nd that itsvpresence is advantageous `in that it expedites the separation of the alkyl ester of thioldimethylvaleric acid from the alkali saltV of dimethylvaleric acid. As examples of the neutralsolvents which We may employ may be mentioned ethyl ether, benzene, toluene, xylene, cyclohexane, and the like. After thoroughly agitating the mixture thus formed, the solvent phase, which also may be referred to as the organic phasacontaining the alkyl ester of thioldimethylvaleric acid is separated from the aqueous phase containing the alkali metal salt of dimethylvalericacid. The solvent phase is then washed with ammonium hydroxide and then with Water until neutral. The solvent may then be removed by distillation andthe remaining solution fractionated to obtain the desired alkyl ester of thioldimethylvaleric acid.

'Theaqueous phase from above which contains the alkali metal salt of dimethylvaleric acid and from which dimethylvaleric acid may be recovered may be treated with a mineral acid until it is distinctlyacid whereupon an oily layer is formed. The oily layer contains L4-dimethylvalerio acid. The aoidiied mixture may then be steam-distilled to obtain an aqueous distillate from which 4,4-dimethylvaleric acid may be recovered in any suitable manner, such, for ex- 4 ample, as by solvent extraction or by azeotropic distillation.

The following example will illustrate the preparation of an alkyl ester of thioldimethylvaleric acid, methyl 4,4dimethyl-thiolpentanoate, in accordance with our invention.

Example I Approximately 40.8 grams (0.2 mole) of the compound CeHizSa melting at about 87 C. and 64 grams (1.6 moles) of sodium hydroxide dissolved in 2 liters of water were placed in a flask iitted with a stirrer and a redux condenser. The CH12S3 compound was the orange-colored crystalline product identiiied as 4-neopentyl-1,2- dithia4-cyclopentene-3-thione. This compound was separated by fractional crystallization from the product obtained by reacting diisobutylene with sulfur at a temperature of about 170 C. and under a pressure of about 150 pounds per square inch. The mixture of CHizSs compound and aqueous sodium hydroxide was heated with stirring at reiiux temperature for about two hours, after which the mixture was cooled to room temperature. To the cooled hydrolyzed reaction mixture thus formed was then added with stirring a mixture consisting of 208 grams (1.6 moles) of dimethyl sulfate dissolved in 50 cc. of ethyl ether. The ether phase containing the methyl ester of thioldimethylvaleric acid was separated from the aqueous phase.(I) and the aqueous phase (I) was extracted with two 100 cc. portions of ethyl ether. The ether extracts were then combined, washed with ammonium hydroxide, and then with water until neutral. The ether was then removed by distillation and the remaining solution was subjected to fractional distillation, whereby there was obtained a fraction boiling at 188 to 194 C. at 744 mm. pressure. This was refractionated and a fraction having a boiling point of 194 C. at 744 mm. pressure was analyzed and was found to be methyl 4,4-dimethyl-thiolpentanoate- The ultimate analysis of the product compared favorably with the calculated analysis for methyl 1 By diierence.

In the above example we have illustrated the preparation of the methyl ester of thioldimethylvalerio acid by rst hydrolyzing the CsHizSa compound With caustic and then adding the hydrolyzed reaction mixture thus formed to an ethereal solution of dimethyl sulfate. It should be understood, however, that the dimethyl sulfate in a relatively high-boiling neutral solvent, such as xylene, andthe aqueous solution of caustic may be added simultaneously to the CaHrzSa compound without deviating from the scope of our invention.

As mentioned hereinbefore, Where it is desired to obtain high yields of the alkyl ester of thioldimethylvaleric acid,4 from a given amount of sulfurized diisobutylene, the aqueous phase remaining after extracting the alkyl ester of thioldimethylvaleric acid from the reaction mass re- 4rsultingrnroin theftreatment. Yoir-the" crude hydrolyzedireactionproductwith an alkyl sulfate, may be` acidified withk a mineral acid,.isteamzdistil-led, treated with'thi'onylzchloride andthe `with the 'corresponding salkyl mercaptan. For example, the aqueous phase il) from above may: bezacidiilied'with sulfuric acid whereby anoily layeris formed. .The v'oily layer may-then 'be removed from'the re'actionmass bysteam distillation. :The oily'lay'er ofthe distillate-so obtained may then -be decantedr-andthe:aqueous.layerextracted with diethyl ether. The ethereal.'extract mayfthen be combined with the .oily'layer yand the combined .product ydried over `anhydrous sodium .sulfate and flnallyjfractionally distilled. After removal of thefetherraction a light straw-.colored liquid fraction.'distilling at1200" to 215 C. may be .obtained. Thisproduct -consists essentially of 4,4- dimethylvaleric'acid. The acid thus formed may then be lconverted toits alkyl `thiol-,ester inaccordance with la .conventional process as exempliedsby the following Example.

Example .II

Approximatelyl jgrams. of 4,4-dimethylva1eric acid 'was' placed in`a1ask,' after which 12 grams of 'thionyl chloride was added. The reaction mixture'thus iormedvvas maintained at a temperature of about 80 C.1until hydrogen chloride was 'no longer '.evolved. The acid chloride thus formed wasthen recovered by distillngthe mixture and collecting the fraction which distilled over at '145 to' 152 C. Y'Eight jgrams of the acid chlorideobtained by 'distillation was then added dropwiseto a mixture consisting of 8 grams of pyridine and `6 grams di methyl mercaptan ata temperature of about -3.0 C. Thel pyridine takes uphydrogenchloride released in the reaction. While itis advantageous to carry out this reaction in -the presence of pyridine. at a temperature of about -'30 C. in order to obtain good yields of the desired product, the process could have been carried out at higher or lower temperatures in the presence of other basic substances such as dimethylaniline, trimethylamine, and the like. vWhen addition of the acid chloride was complete vthe mixture was allowed to gradually Warm up to room temperature, at which `,tern-- perature it was allowed to remain for three days. The mixture was then washed with a sodium bicarbonate solution and then with water to free the ester of contaminants. The methyl ester of thioldimethylvaleric acid was then recovered by distillation. The fraction boiling at 195 C. at 745 mm. pressure was collected as the methyl ester. 'Ihe ultimate analysis of this fraction compared favorably with the theoretical ultimate analysis for methyl 4,4dimethyl-thiolpentanoata as evidenced by the data in the following table.-

The product obtained in accordance with Example II may be combined with the product obtained from Example I, thus giving a high yield of methyl 4,4-dimethyl-thiolpentanoatev from a given amount of sulfurized diisobutylene.

f *Whilefthev preferred-embodiments 'and'ispecinc examples 'of 'qur'f-invention'vhave mentioned only nafdlalkylfsulfateasthe-alkylating agent.v itf'should berunderstood'that we may employ the less `effecvwiltlixeference #to certain` specific examples and embodiments. itwill'fbe understoodthat the inventionlisnctlimitedto-suchillustrated examples andfembodimentsfandimaylbe variously practiced Within lthe vscope 'of :the claimsV hereinafter made.

1. A process *for fthe-1production lof :an alkyl ester oI-'thioldimethylva-leric 'acid 'which compriSesreact-ingthe crude reaction productr resulting "from Athe hydrolysis 'of 4-'neopentyl-L2- 'dithia-4-cyclopentene3-thione with -an alkyl sulfate; andfseparately' recovering from the yreaction'massthus 'obtained an alkylester of-thioldimethylvaleri'c acid.

v2. The iprocess 'of 'claim 1 `wherein 'the Valkyl sulfate is 'a Idialkyl "sulfate containing lnot Amore than Y 6- carbon'v atoms' per l'alkyl group.

"ivlhepro'cess'of claim flvvherein said dialkyl sulfate-contains at least fone `primary-alkyl group.

4.' The/process 'of claim i3 wherein-'the lprimary alkylgroup 'is Ia 'methyl group.

l15. 'The;process"o`f claim 2 'wherein said dialkyl sulfate "contains at 'least'onefsecondary alkyl group. l

6. The process of claim 5 wherein the secondary 'alkyl group bis anV isopropyl group.

7. A process *for the `production of an alkyl `ester of "thioldimethylvaleric acid which comprises 'hydrolyzing i-'ne'opentyl-1,2-dithia-4- cyclopentene-'S-thione, 4thereafter kreacting the hydrolyzedproductrvvith anjalkyl sulfate, said alkyl-'sulfatecontainingnot lmore than 6 carbon atoms; per Aalkyl group, and'separately recovering" from thereaction 'mass Vthus obtained an alkyl ester v'of thioldimethylvaleric acid.

``S55-ri process for 'the k production vof van alkyl Yester ofV 1thioldixneth'ylvaleric acid A`which comprises reacting l'the `product resulting from the hydrolysis of 'lneopentyl1,2-dithia-lcyclopentene-B-thione with an alkyl sulfate in the presence of a neutral solvent, said alkyl sulfate containing not more than 6 carbon atoms per alkyl group, whereby a solvent phase and an aqueous phase are formed, and separately recovering an alkyl ester ofv thioldimethylvaleric acid from the solvent phase.

9. A process for the production of an alkyl ester of thioldimethylvaleric acid which comprises reacting the product resulting from the hydrolysis of 4-neopentyl-LZ-dithia-4- cyclopentene-S-thione with an ethereal solution of an alkyl sulfate, said alkyl sulfate containing not more than 6 carbon atoms per alkyl group,

whereby an ether phase and an aqueous phasel are formed, and separately recovering an alkyl ester of thioldimethylvaleric acid from the ether phase.

10. A process for the production of the methyl ester of thioldimethylvaleric acid which comprises reacting the product resulting from the hydrolysis of 4-neopenty1-1,2-dithia-icyclopentene-S-thione with an ethereal solution of dimethyl sulfate whereby an ether phase and an aqueous phase are formed, separating the ether phase from lthe aqueous phase, removing the ether from the ether-phase -by distillation, and fractionating rthe detherized-solution to obtain the methyl ester of thioldimethylvaleric acid boiling at about 194 C. at 744 mm. pressure.

l1. A ,processi for the production Vof an alkyl ester of thioldimethylvaleric acid which comprises heating .4-neopentyl-l,2-dithia-flcyclopentene-B-thione .with va reactant mixture consisting of an aqueous solution of an alkali metal hydroxide, a high boilingneutral solvent and an alkyl sulfate until reaction is ysujtstantially complete whereby a solvent phase and an aqueous phase are formed, separating the solvent phase from theaqueous phase, and separately recovering the alkyl ester of thioldimethylvaleric acid from the solvent phase.

l2. A process for the production of the methyl ester of thioldimethylvaleric acid. which comprises heating 4neopenty11,2-dithia-4-cyclopentene-Z-thione With an aqueous solution of an alkali metal hydroxide at reux temperature until reaction is substantially;A complete, thereafter cooling the reaction mixture to a temperature of about 20 to 30 C., treating the cooled reaction mixture with an ethereal solution of dimethyl sulfate, the dimethyl sulfate being added in an amount equimolar to the amount of said alkali metal hydroxide employed whereby an ether phase and an aqueous phase are formed, separating the ether phase from the aqueous phase, removing the ether from the ether phaseby distillation, and fractionating the de-etherized solution to obtain the methyl ester of thioldimethylvalerio acid boiling at about 194 C. at 744 mm. pressure.

13. A process for obtaining increased yields of the methyl ester of thioldimethylvaleric acid from 4-neopentyl-l,2-dithia-4-cyclopentene-3- thione which comprises hydrolyzing the l-neopentyl-1,2dithia-4-cyclopentene3-thione with an aqueous solution of an alkali metal hydroxide, cooling the reaction mixture thus obtained to a temperature of about 20 to 30 C., treating the cooled reaction mixture with an ethereal solution of dimethyl sulfate, the dimethyl sulfate being added in an amount equimolar to the amount of said alkali metal hydroxide employed whereby an ether phase and an aqueous phase are formed,

ioy

separating the ether phase from the aqueous phase, removing the ether from the ether phase by distillation, fractionating the de-etherized solution to obtain the methyl ester of thioldimethylvaleric acid, acidifying'said aqueous phase with a mineral acid until separation of the organic acids in the form of a supernatant oil is substantially complete, steam-distilling said oil from the acidied mixture, separately recovering from said oil a fraction distilling at 200 to 215 C. consisting essentially of 4,4-dimethylvaleric acid, reacting the 4,4-dimethylvaleric acid thus formed with thionyl chloride, recovering the acid chloride of 4,4-dimethylvaleric acid by distillation, thereafter slowly adding said acid chloride to a mixture of pyridine and methyl mercaptan and separating the methyl ester of thioldimethylvalerio acid from the mixture thus formed.

14. A process for the production of the methyl ester Vof thioldimethylvaleric acid which comprises heating Ii-neopentyl-1,2-dithia-4-cyclopentene-S-thione with an aqueous solution containing from about 4 to 8 moles of sodium hydroxide in a concentration of from about 0.5 to about 50 per cent by weight at reiiux temperature until reaction is substantially complete, thereafter cooling the reaction mixture to a tempera-ture of about 20 to 30 C. and adding an ethereal solution of dimethyl sulfate, the dimethyl sulfate being added in an amount equimolar to the amount of said sodium hydroxide employed, whereby an ether phase and an aqueous phase are formed, separating the ether phase from the aqueous phase, removing ether from the ether phase by distillation, and fractionating the de-etherized solution to obtain the methyl ester ofthioldimethylvaleric acid.

RODERICK S. SPINDT. DONALD R. STEVENS.

REFERENCES CITED The following references areo record in the le of this patent:

UNITED STATES PATENTS 

1. A PROCESS FOR THE PRODUCTION OF AN ALKYL ESTER OF THIODIMETHYLVALERIC ACID WHICH COMPRISES REACTING THE CRUDE REACTION PRODUCT RESULTING FROM THE HYDROLYSIS OF 4-NEOPENTYL-1,2,DITHIA-4-CYCLOPENTENE-3-THIONE WITH AN ALKYL SULFATE, AND SEPARATELY RECOVERING FROM THE REACTION MASS THUS OBTAINED AN ALKYL ESTER OF THIOLDIMETHYLVALERIC ACID. 